It is known to protect various thermoplastic resin compositions against fungal or bacterial attack by incorporating a microbicide therein to prevent the deterioration of articles formed from the resin compositions. Microbicide inhibit growth of bacteria or fungi by acting upon the cell wall or upon cell proteins, e.g., by attacking disulfide bonds. In order for the microbicide to be effective in the resin composition, it is necessary that it be compatible with the components of the resin composition and be uniformly dispersible in the resin composition. The microbicide must be carried by the resin composition in a manner that it remains biologically active against microorganisms, and, in particular, must be available at the surfaces, including internal pore surfaces. Incorporation of microbicides in resin compositions is generally effective only in compositions in which the microbicide is able to slowly migrate to the surfaces. In some cases, the microbicide migrates slowly through amorphous regions of the polymer. In other cases, biocide migration is facilitated by plasticizers which are included along with the polymeric resins in end-use resin compositions. As the microbicide at the surfaces in used up through action against microorganisms, additional microbicide migrates to the surfaces. Although a microbicide may be a highly toxic chemical, its low concentration in the end-use product and its retention by the resin composition ensures that the microbicide in the end-use product poses no hazard to humans or animals.
Microbicides must be available in a form that is readily dispersible into the formulation mix from which the end-use resin composition is fabricated. The powdered or crystalline form in which many useful microbicides are commercially available are readily dispersible; however, at the site of mixing, powdered or crystalline microbicides pose a substantial environmental and health hazard if powder or crystal fines are dispersed into the atmosphere. Furthermore, powder, or powdered fines, if dispersed into the atmosphere, represent a potential explosive hazard.
Recognizing the toxicity problem of microbicides in powder or crystalline form, U.S. Pat. No. Re. 29,409 teaches dissolving microbicides in liquid solvents which may be added to the formulation mixture from which the end-use resin compositions are fabricated. Although liquid dispersions may be safely used at the site of preparing end-use resin compositions, careless use or disposal of the liquids may still pose environmental and health hazards.
U.S. Pat. No. 4,086,297 issued Apr. 25, 1978 to Rei, et al., the teachings of which are incorporated herein by reference, describes solid thermoplastic microbicide resin concentrates containing immobilized microbicides. These solid microbicide resin concentrates contain relatively high concentrations of microbicides and may be added to the formulation mixtures from which the end-use resin compositions are prepared in an amount sufficient to provide the desired end-use microbicide concentrations. The solid microbicide resin concentrates, which are typically provided in the form of small pellets, can be handled freely, posing substantially no health or environmental threat. Such pellets are even safe for direct skin contact. Although microbicides are sufficiently immobilized and inactive in the solid microbicide resin concentrates, in softer end-use resin compositions, the low concentration microbicides at the surface have biological activity, and gradual and continuous migration to surfaces ensures continuous biological activity. Where practical, a solid microbicide resin concentrate represents a preferred manner of providing a microbicide to producers of end-use thermoplastic products.
U.S. Pat. No. 4,789,692, the teachings of which are incorporated herein by reference, discloses blends of polymers and also copolymers and terpolymers that are particularly suitable for carrying concentrated levels of microbicides into particular thermoplastic resins.
In order that inclusion of a microbicide impart biocidal activity to an end-use product, the microbicide must be available at the surface to act against microbial growth. In a flexible end-use composition, which comprises a thermoplastic resin and a plasticizer, the plasticizer commonly provides the transport mechanism for continual replenishment of incorporated microbicide to the surface of the end-use article. A typical product of this nature is a polyvinyl chloride (PVC) shower curtain which contains substantial amounts of plasticizer and sufficient microbicide to protect the shower curtain from microbial attack for an extended period of time.
On the other hand, rigid polymeric materials may be afforded substantially no protection by the inclusion of microbicides because the incorporated microbicide does not migrate to the surface where it is available to act against microbial organisms. An example of this is rigid PVC, such as that for siding of houses. Unlike flexible, plasticized PVC compositions, rigid, non-plasticized PVC is not particularly subject to degradation by microbial attack. Nevertheless, microbial growth on the surface of such rigid polymeric material is undesirable, particularly from an aesthetic standpoint.
It is a primary object of the invention to provide solid concentrates of microbicides-in-resins that can be used to provide biocidal activity to rigid thermoplastic resins. Other objects and advantages will become more fully explained in the following description of the invention.